The keymap.transfer command is only useful if we have both PROGMEM & EEPROM
keymaps, which will rarely be a case, and likely only temporarily, too. As such,
lift that out of the `focusKeymap` function, into its own. This makes the
command optional, and can save us some 140 bytes of program space (even more if
documentation is enabled).
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>